Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$129.44	7.711%	$139.4211	$139.42	$139.40	$139.40
Purchase #2	$90.45	7.859%	$97.5585	$97.56	$97.55	$97.60
Purchase #3	$18.86	8.741%	$20.5086	$20.51	$20.50	$20.50
Purchase #4	$235.39	13.248%	$266.5745	$266.57	$266.55	$266.60
Purchase #5	$155.58	11.285%	$173.1372	$173.14	$173.15	$173.10
Purchase #6	$247.54	5.213%	$260.4443	$260.44	$260.45	$260.40
Purchase #7	$85.68	5.212%	$90.1456	$90.15	$90.15	$90.10
7 purchase totals =	$962.94		$1,047.7898	$1,047.79	$1,047.75	$1,047.70